It is described in the 2013 edition of ITRS (International Technology Roadmap for Semiconductors) Metrology Summary that FinFETs are now the dominant key element architecture of advanced microprocessors and both FinFETs and other three-dimensional structure measurement technologies are facing the challenges of reduced size and increased aspect ratio.
Current nanoscale measurement instruments such as CD-SEMs and CD-AFMs only provide a two-dimensional (X-axis and Y-axis) measurement of a surface structure, which are limited in providing a third dimensional (Z-axis) measurement. Therefore, dimensions such as the line width, the height and the sidewall angle of a three-dimensional structure having a high aspect ratio cannot be obtained. To overcome the drawback, a measurement method is proposed. A conventional measurement method involves emitting a light beam from a light source generator onto an object through a light focusing element. Then, the light beam passes through a lens and is collected by a camera. With the rotation of a prism, the incident angle of the light beam incident on the object is changed. The light beam is scattered and dispersed by the object to generate multi-order diffraction signals, and zero-order (0th-order) signals of the multi-order diffraction signals are measured. Based on the correlation between the 0th-order signals and the incident angles, a feature spectrum is generated to facilitate analysis of the three-dimensional structure of the object. However, in the above-described measurement method, an error of the rotating mechanism appears in the measurement result. In addition, the measurement process is time-consuming. According to another conventional measurement method, a light beam from a broadband light source is incident on an object with a fixed angle. The light beam is then scattered by the object to generate multi-order diffraction signals. 0th-order signals of the multi-order diffraction signals are captured and then dispersed by a spectrometer. As such, the distribution of diffraction intensities at different wavelengths is measured to facilitate analysis of the three-dimensional structure of the object. However, after the light passes through a dispersive element and a slit of the spectrometer, the light intensity decays significantly that adversely affects the measurement accuracy. Therefore, in the above-described measurement methods, the measurement accuracy is reduced either by an error of the rotating mechanism or by a significant decay of the light intensity after the light passes through a dispersive element.
Therefore, if the three-dimensional structure of an object (including the Z-axis dimension) can be quickly and accurately measured based on a theoretical model of a laser light scattering device and hardware experiences with the laser light scattering device as well as EUV (extreme ultraviolet) scattering device technologies, measurement of future nanoscale objects will be facilitated. It has become urgent to solve this issue.